Overpass API
OpenStreetMap's public query interface — ask it for every tagged building or road inside a bounding box and it returns the live map data.
It's how the v1 CBD scene was built, and it's free — but it only returns what volunteers have traced.
{# Definition → argument. Same word-boundary match that places the inline hover in the reader, so this list is exactly where the term is explained on the page. #}
Where it comes up
Other concepts